Correct terminology of "Unique Opens" and "Total Opens", docs was using old...

Correct terminology of "Unique Opens" and "Total Opens", docs was using old terminology and did not explain Unique Opens at all.

docs/email/reports-and-analysis.md

@@ -23,8 +23,11 @@ contacts that took the action.
 **Intended Recipients** shows the number of people that the mailing was
 intended to be sent to. 
 
-**Tracked Opens** shows the number of people that CiviCRM thinks have
-opened the email *if you have chosen to track opens*.
+**Unique Opens** shows the number of people (or bots) that CiviCRM thinks have
+opened the email if you have chosen to enable *Open tracking*.
+
+**Total Opens** shows the total number of times that CiviCRM thinks people (or bots) have
+opened the email if you have chosen to enable *Open tracking*.
 
 !!! info "How Open Tracking works"
     In the world of email, there is no 100% reliable way of